It has been suggested that the non-acute failure of synthetic small diameter arterial bypass grafts is related to their lower distensibility, or circumferential compliance, compared to that of the host arteries. Based on inconclusive experimental evidence and on theoretical grounds, large commitments have been made to manufacture a compliance synthetic graft. But studies of stiffened autogenous grafts suggest that compliance may be inconsequential in the absence of the thrombogenic surface. Other data suggest compliance becomes irrelevant after an acute period. The true importance of graft complaince is thus still unclear. The hypothesis that compliance affects the outcome of arterial grafts, will be tested in dogs by comparing identical compliant femoral arterial grafts, one of which will be stiffened by external banding. A new banding method will ensure that changes in circumferential and longitudinal distensibility will occur sharply at the anastomoses, as occurs with synthetic grafts in clinical use. Surface thrombogenicity will be varied by using carotid arteries or polyurenthane as grafts, with or without inducing uniform injury to endothelial surfaces in the graft and/or adjacent arteries. The influence of length, in synthetic grafts up to 50 cm long will also be studied. Changes in compliance with time will be followed noninvasively using pulsed ultrasound. Surfaces will initially be analyzed by infrared spectroscopy, critical surface tension and x-ray dispersion analyses. The acute deposition of In-111-labeled platelets will be quantified by autoradiography, and chronic changes in surface properties or intimal thickness will be evaluated by histology and morphometry, surface analysis and scanning electron microscopy. If the hypothesis is proven, the mechanisms by which mechanical properties influence graft patency will be investigated, and methods to ameliorate the adverse effects of compliance mismatch to improve clinical results with grafts will be explored. A more complete understanding of the biological response to imcompliant grafts will assist in the development of improved vascular prostheses.